Yes, yet another Double Dragon repair log..

Found this PCB in the pile, honestly I can’t remember when and where I got it :

Once powered ON I was greeted by this title screen:

Also sprites in game were all blocky with some parts floating on the screen:

I also noticed that some sound FXs (especially speeches) were missing so I decided to first troubleshoot this issue.Probing one of the OKI MSM5205 @IC81 I found that all four data outputs were not toggling.The chip read data from the two samples EPROMs not directly but through two 74LS157 multiplexers.I found that select line (PIN1) of the one @IC96 was stuck HIGH so data inputs were not selected at all.I traced it back to an output  (PIN3) of the 74LS393 @IC62 so I desoldered it but it was good.Probing the its CLEAR pin I found that it was stuck HIGH.Tracing it back lead me to an output (PIN6) of a 74LS74 @IC75. I desoldered it and tested it out-of-circuit  having confirm that it was bad:

With sound FXs fully restored I decided to come back to the sprites issue.Fault was located in the VIDEO board since I swapped a good one and issue sprites came back normal.Luckily we have schematics so I started to check for parts of circuits involved in the sprite generation and handling but after two days of troubleshooting and a lot of suspected ICs replaced in vain I came to a dead end.I was nearly to give up and declare the board as not repairable but checking the last part of the object generation schematics I found a missing signal input (called ‘OCGL’) on PIN9 of a 74LS08 @IC36.This signal is generated by an output (PIN5) of a 74LS174 @IC69 always on VIDEO  board.

As I said this ‘OCGL’ signal was present as output of the 74LS174 but not as input of the 74LS08 so it was lost somewhere on the PCB.Following on solderside the traces between these two ICs I came across a via under a 74SL157 @IC34.I desoldered it and found this:

Oxid literally had corroded and eaten the pad and part of trace thus preventing the ‘OCGL’ signal reaching the input of the 74LS08.A tiny piece of AWG30 wire:

and Billy e Jimmy Lee bros could fight again!

 

Another board donated from my arcade operators friends.It’s time for Crime City.

For the uninitiated, Crime City is a beat ’em up developed by TAITO that can be played by one or two players simultaneous.Here are the technical specs of the hardware:

• Hardware – Taito System B Hardware
• Board Number – K1100470A
• Main CPU – 68000 (@ 12 Mhz), Z80 (@ 4 Mhz)
• Sound – YM2610 (@ 8 Mhz)
• Screen Orientation – Horizontal
• Resolution – 320 x 224
• Refresh Rate – 60 Hz
• Palette Colors- 4096
• Players – 2
• Buttons – 2
• Joystick – 8 way

The board booted fine but I immediately noticed that there was no sound at all except for some scratching noises.Besides, some colours were wrong and some characters tended to pink compared to the correct ones from MAME (see wheels of car in the picture below, MAME screenshot is on the right) :

 

As usual I started my troubleshooting with a visual inspection of the PCB and found a broken track on the solderside which I promptly patched with some AWG30 wire:

This fix restored correct colours (the broken track was actually connected to the TAITO ASIC TC0260DAR which is a custom pallette generator and this explained the reason of the fault)

As I said board was silent, no sound at all except for some noise sign that the main MB3735 amplifier was working fine.Digital audio section is made by a Z80 CPU which commands a sound synthesis YM2610 chip.With my logic probe I could verify that all was working fine there so fault was elsewhere.So I started to suspect the YM3016F sound DAC:

Connecting its analog output to an external amplifier produced no sound (while digital input was present).This convinced me to replace it and so sound was fully restored .

First of all I wanna thank the people who donated me this (and other) PCB : “mille grazie” to Mr. Giuseppe (a long-standing arcade operator of my town) and his nice daughters Elena and Antonella!

Now, let’s begin with the log.

When I got  this PCB in my hands, I immediately tought it was a Rainbow Islands one:

But I was wrong, it actually was the Extra version (different ROMs and C-Chip).Before start the troubleshooting, I resoldered a wonky TC0070RGB module:

Once powered on, I got a solid white screen with a clicking sound indicating that the watchdog circuit was active:

There was clearly some trouble in main code execution so I started to test with my logic probe the two WORK RAMs  and I found some data lines stuck HIGH on the 6264 SRAM @IC25.I desoldered the chip and out-of-circuit test confirmed it as bad:

With a new RAM the board succesfully booted but graphics (tiles and sprites) were all blocky:

 

This board (and other Taito ones on similar hardware ) uses two custom chips  in PGA package which generates sprites (the one marked ‘PC0900J’) and tiles (the ‘PC080SN’).They respectively address GFX ROMs through a couple of  74LS373 latches.Probing the 74LS373 @IC29 I found that all the outputs were absent.So I piggybacked a good one and tiles were restored but sprites were always blocky:

 

So, I went through the 74LS373 @IC18 and found it had output PIN19 stucked LOW while its input was toggling.Piggybacked this and also sprites were restored.Desoldered the two 74LS373 and they were indeed bad:

Replacing them both back this game to its former glory!